The present invention relates to a new class of metal:carbon molecular structures known as metallo-carbohedrenes (Met-Cars), and preparation and characterization of same. These molecules have potentially a variety of applications including use as new electronic materials and as catalysts.
By way of background, the reported observation of the molecule C.sub.60 [Kroto, H. W., et al., Nature 318, 162 (1985)] [Curl, R. F., et al., Science 242, 1017 (1988)] has prompted extensive activity in fullerenes and related carbon-cluster research [Weltner, Jr., W., et al., Chem. Rev. 89, 1713 (1989)] [Kroto, H. W., et al., Chem. Rev. 91, 1213 (1991)]. A group at AT&T Bell Laboratory reported the successful doping of alkali metal atoms into C.sub.60 crystals to produce a new superconductive material [Hebard, A. F., et al., Nature 350, 600 (1991)]. Smalley and coworkers obtained evidence for the incorporation of lanthanum in the interior of C.sub.60 [Chai, Y., et al., J. Phys. Chem. 95, 7564 (1991)], a structure which has been born out by more extensive studies. Also, other researchers have reported the ability to incorporate He+ within the fullerene ball [Weiske, T., et al., Angew. Chem. Int. Ed. Engl. 30, 884 (1991)] [Ross, M. M., et al., J. Phys. Chem. 95, 5720 (1991)]. In addition to the above doping, Smalley's group [Guo, T., et al., J. Phys. Chem. 95, 4948 (1991)] has found that a few carbon atoms in C.sub.60 can be replaced by non-metal boron elements in the C.sub.60 cage without substantially destabilizing the entire fullerene.
Currently, there is extensive interest in the prospect of producing new materials comprised of molecular clusters. This is evidenced by the explosive research on C.sub.60. Interest in these materials has arisen due to the fact that molecular clusters often display unique physical and chemical properties unlike those of other forms of matter.
We discovered a remarkably stable cluster Ti.sub.8 C.sub.12.sup.+ (C. Guo, K. P. Kerns, and A. W. Castleman, Jr., Science 255, 1411, 1992) and postulated that its extraordinary stability was due to geometric and electronic properties inherent in a cage-like, suggested dodecahedral structure. Furthermore, we suggested that this molecule might be just one member of a new general class of molecular clusters named as metallo-carbohedrenes or Met-Cars which involve possible incorporation of early transition metals with carbon to construct a cage like-structure. Thereafter, our subsequent work confirmed this speculation and revealed that other early transition metals such as vanadium, zirconium, and hafnium can form similar stable metallo-carbohedrenes, M.sub.8 C.sub.12, as well (B.C. Guo, S. Wei, J. Purnell, S. Buzza, and A. W. Castleman, Jr., Science, 256, 515, 1992 and S. Wei, B.C. Guo, J. Purnell, S. Buzza, and A. W. Castleman, Jr., J. Phys. Chem., 96, 4166, 1992)
The observation of Met-Cars and their proposed structure has received favorable response from the chemistry, physics, and materials science communities. Just a few months after our first report on Met-Cars, intensive theoretical investigations to verify our findings were made by a number of research groups [B. V. Reddy, S. N. Khanna, and P. Jena, Science, 258 1640 (1992), R. W. Grimes, and J. D. Gale, J. Chem. Soc., Commun., 1222, 1992, Z. Lin, and M. B. Hall, J. Am. Chem. Soc 114, 10054 (1992). B. V. Reddy, S. N. Khanna, and P. Jena, Science, 258 1640 (1992). R. W. Grimes, and J. D. Gale, J. Chem. Soc., Commun., 1222, 1992.., Z. Lin, and M. B. Hall, J. Am. Chem. Soc 114, 10054 (1992)., M. M. Rohmer, P. De Vaal, and M. Benard, J. Am. Chem. Soc. 114, 9696 (1992), M. Methfessel, M. van Schilfgaarde, and M. Scheffer, Phys. Rev. Lett. 70, 29 (1992), A. Ceulemans, and P. W. Fowler, J. Chem. Soc. Faraday Trans., 88, 2797 (1992), L. Pauling, Proc. Natl. Acad. Sci., 89, 8175 (1992). These calculations suggested that Met-Cars with a cage-like structure are indeed very stable and that they are assembled by a framework comprised of metal-carbon and carbon-carbon bonds.
The main difference between Met-Cars and the well-known buckyball C.sub.60 is that the structure of Met-Cars is constructed with metal-carbon and carbon-carbon bonds, while that of C.sub.60 is built with only carbon-carbon bonds. In view of this difference, it is considered likely that Met-Cars will display significantly different chemical properties from those of C.sub.60.
This novel kind cage-like molecules which we term metallo-carbohedrenes, in which a number of metal atoms incorporate with carbons to form a symmetrical network, have not been described heretofore.